1. Field of the Invention
The present invention relates to a pixel and an organic light emitting display device including the same.
2. Description of Related Art
Recently, various flat panel display devices having light weight and small volume, as compared to cathode ray tubes, have been developed.
Among the flat panel display devices, organic light emitting display devices have excellent brightness and color purity by displaying images using organic light emitting diodes, which are self-emission devices. Therefore, they are in the spotlight as next generation display devices.
Such organic light emitting display devices can be categorized as passive matrix type organic light emitting display devices and active matrix type organic light emitting display devices, depending on a scheme for driving the organic light emitting diodes.
The active matrix type organic light emitting display device includes a plurality of pixels positioned at crossing points of scan lines and data lines. Each of the pixels includes an organic light emitting diode and a pixel circuit for driving it.
The active matrix type organic light emitting display device has a small power consumption so that it is useful for a portable display device, etc.
However, the active matrix type organic light emitting display device has a disadvantage in that its picture quality becomes non-uniform as a result of brightness differences between pixels generated due to threshold voltage variation of driving transistors.
Therefore, pixel circuits of a variety of structures have been suggested to compensate for the threshold voltage variation of the driving transistors. Currently, a pixel structure adopting a compensating transistor coupling the driving transistor to the diode during a predetermined period is well known.
However, in the case of compensating for the threshold voltage by coupling the driving transistor to the diode, a signal may not be normally written according to a voltage level of a data signal supplied for every frame.
For example, when the voltage level of the data signal supplied in a current frame is lower than that of the data signal supplied in a previous frame, a direction in which the driving transistor is diode-connected may be reversely set so that the data signal may not be written in the pixel.
Therefore, in order to prevent this, it is desirable to efficiently initialize each of the pixels before writing the data signal.
However, in the case of coupling a separate initialization power supply to each of the pixels for such an initialization, the number of signal lines within a display unit can increase.
Also, since the initialization is generally performed while a previous scan signal is being supplied, each of the pixels is coupled to a current scan line as well as a previous scan line. Therefore, two scan line portions are disposed at a region in which each of the pixels is located.
Accordingly, in a conventional organic light emitting display device, an aperture ratio is reduced and there is a spatial limitation associated with pixel formation.
Also, in the conventional organic light emitting display device, portions of the two scan lines are disposed in each of the pixels so that one terminal of a scan driver should drive the two scan lines. Therefore, since a load applied to each terminal of the scan driver increases, an internal circuit of the scan driver should have sufficient capacity to be able to cope with this.